Death of an Engineer

A doctor, a lawyer, and an engineer are all scheduled for execution on a guillotine. As they step up to the scaffold, each is given a choice of lying face up or face down. The doctor goes first, and believing that one should confront one's fate directly, he opts to lie face up. The blade drops but then screeches to a stop just a foot above the doctor's throat. Amid the gasps of the crowd, the doctor is released.
The lawyer goes next. She is sure that legal precedent would lead to her own release were the blade to stop for her just as it had for the doctor, so she also lies face up. Again the blade stops short, and the lawyer is released.
Now its the engineer's turn. He figures that his best bet is to go with whatever worked before. So he lies face up and sees the blade overhead. But then, just before the blade is drops, he turns to the executioner and says, "Wait! I think I see what your problem is up there."